The reaction of phenol and ammonia in vapor phase over acid catalysts has been described as early as 1933 in U.S. Pat. No. 1,935,209. A series of relevant patents has evolved, including U.S. Pat. Nos. 2,013,873, 3,272,865, and 3,578,714. A process flowsheet was published by M. Becker et al (Chemical Engineering, Apr. 2, 1973, pp 42-43) describing a process for making aniline by the reaction of phenol with an excess of ammonia over a catalyst made up of aluminas derived from precipitated gels containing less than 1% alkali metal and having surface areas of more than 150 sq. meters per gram.
The commercialization of this process resulted from two discoveries which are described in U.S. Pat. Nos. 3,860,650 and 3,682,782. The '782 patent describes the recovery of high purity aniline from aniline-phenol mixtures. Crude aniline containing low residual phenol is needed, as phenol and aniline have close boiling points and also form an azeotrope. Such crude is obtained at low LHSV over a high activity catalyst. The '650 patent describes the catalytic part of the process which is carried out over acid washed H-151 alumina, manufactured by Alcoa (Activated and Catalytic Aluminas, Brochure published by Alcoa Chemicals, Oct. 1, 1961), a desiccant alumina derived from a precipitated gel.
The '650 patent describes also the procedure of leaching H-151 with aqueous acid solutions to remove sodium, which is imperative for achieving relatively high catalytic activity. Even though both disclosures permitted successful commercialization, this process is still an unusual vapor phase catalytic technology in that LHSV is adjusted at about 0.04 and an ammonia to phenol mole ratio of about 20 is needed to obtain high phenol conversion and high selectivities to aniline. Higher LHSV which would require higher reaction temperatures are not desirable because of ammonia dissociation to nitrogen and hydrogen. However, low capital costs, the low catalyst deactivation and minimum waste disposal problems are attractive compared to the conventional route of making aniline and, more generally, aromatic amines, from nitrobenzenes. As an environmental matter, a process which does not generate nitrogen oxide compounds is of increasing interest.
Following the implementation of the process, it appeared to the inventors herein that acid washed H-151 alumina is an exceptional catalyst in many ways and attempts to obtain a similar catalyst having at least equivalent activity, selectivity deactivation rate and thermal stability failed for the following reasons:
Silico-alumina catalysts have higher acid strength and produce undesirable by-products. Side reactions also favor the deposit of carbonaceous materials the catalyst which results in high deactivation rates. Such catalysts are described in U.S. Pat. No. 3,272,865.
Binary oxides such as zirconia-alumina, titania-alumina and others reported in Japanese Patents 23,053 and 23,571 are not as active as the acid leached H-151 alumina and deactivate rapidly because of the need of high reaction temperatures.
European Patent 293,483 describes a low alkali alumina catalyst obtained by firing an alumina (H-152 manufactured by Alcoa) at a temperature of 600.degree.-900.degree. C. followed by acid treatment. Although the catalyst shows good catalytic stabilities, its activity is about 70% of the H-151 based catalyst; equivalent performances are obtained at reaction temperatures of about 375.degree. C. compared to 363.degree. C. for the acid leached H-151. The firing treatment is needed to expel the sodium out of the alumina structure which then becomes removable by acid leaching treatments. However, while the removal of sodium is beneficial to the catalytic activity, the calcination at high temperature causes the alumina crystallites to sinter. The surface area, and consequently the catalytic activity are relatively reduced.
Other aluminas such as those obtained by calcination of gibbsite (product of the Bayer process) also contain appreciable amounts of sodium. Although high surface area can be obtained, the sodium is usually difficult to remove. Intensive acid treatments are able to bring the sodium content down to 0.3% Na.sub.2 O but reduce the surface area dramatically. A comparative example is shown in this disclosure.
Gamma aluminas obtained by calcination of pseudoboehmite materials such as Catapal (Vista Chemicals), Disperal and Pural (Condes Chemie), made from aluminum, and Versal 250, 450, 800 and 900 (LaRoche Chemicals), made from sodium aluminate, are low sodium aluminas. Comparative example D of U.S. Pat. No. 3,860,650 reported the test reaction results of such catalysts. It is shown that a reaction temperature of about 410.degree. C. is necessary to obtain 95% phenol conversion. Two disadvantages of such catalysts are their relatively lower surface areas and packed densities.
It is an object of this invention to provide a catalytic process for converting phenols to aromatic amines and in particular phenol to aniline.
It is a further object of this invention to provide a catalyst comparable in activity to one made from the acid leached H-151 alumina.
It is also an object of this invention to provide a catalyst which can be made cheaply and relatively easily with commercially available raw materials.
It is also a further object to provide a method for manufacturing such catalyst with good mechanical properties.